Unit for protecting a metal tube containing at least one optical fiber against internal overheating, and a method of implementing it

Abstract

The unit for protecting the inside of a metal tube containing at least one optical fiber against overheating limits the extent to which fibers inserted by an auxiliary tube and filler gel overheat level with the laser welding that closes the metal tube. The unit including a thermal diffuser interposed between the auxiliary tube for inserting fibers and the closure zone that is defined on the metal tube. The invention is applicable to making an underwater optical cable.

We claim: 
     
       1. A unit for protecting a metal tube against internal overheating at a stationary laser welding station that defines a closure zone on said metal tube which is driven past said station, and that includes at least one first auxiliary tube serving to guide and insert at least one optical fiber in said metal tube so that the fiber extends along the metal tube beyond said closure zone, the unit including a thermal diffuser mounted inside said metal tube and interposed between said first auxiliary tube and said closure zone defined on said metal tube at said laser welding station. 
     
     
       2. A unit according to claim 1, further associated with at least one second auxiliary tube injecting a filler material into said metal tube so that the filler material also extends beyond said closure zone, where said thermal diffuser is carried by said at least one second auxiliary tube and is disposed directly facing said closure zone. 
     
     
       3. A unit according to claim 2, wherein there are two of said second auxiliary tubes extending side by side and separating said first auxiliary tube from said thermal diffuser, and wherein said thermal diffuser is fixed on said two second auxiliary tubes. 
     
     
       4. A unit according to claim 1, wherein said thermal diffuser is a plate of a material that is a good conductor of heat. 
     
     
       5. A unit according to claim 1, further including a device for cooling the outside of said metal tube and mounted directly downstream from said laser welding station. 
     
     
       6. A method of implementing a unit for protecting a metal tube against internal overheating at a stationary laser welding station that defines a closure zone on said metal tube which is driven past said station, said unit including at least one first auxiliary tube serving to guide and insert at least one optical fiber in said metal tube so that the fiber extends along the metal tube beyond said closure zone, the unit including a thermal diffuser mounted inside said metal tube and interposed between said first auxiliary tube and said closure zone defined on said metal tube at said laser welding station, said metal tube being made by deforming an initially flat metal tape, the method comprising the steps of: causing the metal tube as entrained past said laser welding station to have a cross-section that is greater than a final section desired therefor, and wherein said cross-section is egg-shaped having a "top" first half which is substantially circular and on which said closure zone is centered, and a "bottom" second half which is substantially V-shaped with a semicircular bottom of radius smaller than that of said first half and substantially equal to the radius of said first auxiliary tube that is received therein; and   reducing the egg-shaped section and making it circular beyond the ends of the auxiliary tubes within said metal tube.   
     
     
       7. A unit for protecting a metal tube against internal overheating at a stationary laser welding station that defines a closure zone on said metal tube which is driven past said station, and that includes at least one first auxiliary tube serving to guide and insert at least one optical fiber in said metal tube so that the fiber extends along the metal tube beyond said closure zone, and two second auxiliary tubes extending side by side between said first auxiliary tube and said closure zone and injecting a filler material into said metal tube so that the filler material also extends beyond said closure zone, the unit including a thermal diffuser fixed on said two second auxiliary tubes directly facing said closure zone and interposed between said first auxiliary tube and said closure zone. 
     
     
       8. A unit for protecting a metal tube against internal overheating at a stationary laser welding station that defines a closure zone on said metal tube which is driven past said station, and that includes at least one first auxiliary tube serving to guide and insert at least one optical fiber in said metal tube so that the fiber extends along the metal tube beyond said closure zone, the unit including a thermal diffuser mounted inside said metal tube and interposed between said first auxiliary tube and said closure zone defined on said metal tube at said laser welding station, wherein said thermal diffuser is a plate of a material that is a good conductor of heat.